The present invention relates to apparatus and method for generating acoustic energy, and, more particularly, to apparatus and method for generating such energy wherein excitation, or driver, means are not part of, and are not rigidly connected to, acoustic radiating means, so that flexing of the excitation means is substantially reduced and/or eliminated.
As used herein, a transducer is a device capable of being actuated by generating waves from one or more transmission systems or media, and of supplying related generated waves in response thereto to one or more other transmission systems or media. A specific example of such a device is one which receives electrical waves (generating waves) and produces acoustic waves (generated waves) which may be injected into a transmitting medium such as air or water. An audio speaker is an example of such transducer using air as a transmitting medium and a sonar transducer is an example of use with a water medium. The present invention will be described as it may be used with water as a transmitting medium, it being understood that the invention is not limited by the type of transmitting medium used.
In order to create an acoustic wave in a transmitting medium, it is necessary that a portion of the transmitting medium be physically moved. The amount or volume of the transmitting medium moved by the acoustic radiating means per unit time will determine the power of the generated wave, and the rate of a pulsing or oscillation of the acoustic radiating means that imparts such movement will determine the frequency of the generated wave.
In the category of known sonar transducers, there is a group of such transducers that generate acoustic energy by flexure of the acoustic radiating member, which commonly is arranged as a bar or disk that includes the electroactive material, such as a piezoelectric ceramic, used to form the electroactive driver for the radiating member. Thus, for the flexural class of transducers, the acoustic radiating member and the electroactive driver constitute the same element, and the driver is subjected to bending stresses. A representative flexural transducer is shown in the middle figure on page 101 of an article entitled "Low Frequency Sonar Projectors"--Hutchins from Scientific Honeyweller, Fall 1987 (pgs. 96-103).
Another group of known sonar transducers may be classified as flextensional. In flextensional transducers, the electroactive driver is separate from, but rigidly mechanically connected to, the acoustic radiating member.
Regardless of the transducer configuration, imposition of flexing forces and resulting bending stresses on electroactive driver elements limits the instantaneous peak power and average power, of acoustic energy that can be generated by the transducer. Care must be taken not to exceed bending stresses, especially when applied in tension to the driver, which may damage and/or cause catastrophic failure of the driver. A typical acoustic driver may be made up of a plurality of segments of electroactive material, and the loss or failure of even one segment due to mechanical failure may cause severe loss of power handling capability of the entire transducer.
It would be desirable to provide a transducer wherein the driver is not subjected to flexing forces or bending stresses while still able to generate acoustic energy of relatively high power at relatively low frequency. As used herein, low frequency means less than about 1000 Hz, although the present invention is not limited to operation at such frequencies. It would also be desirable to have the acoustic radiating means include a flat member for ease of manufacture and assembly/disassembly of the transducer.
Accordingly, it is an object of the present invention to provide a transducer having electroactive, or other, driver means for generating acoustic energy, wherein the electroactive, or other, driver means are not either part of, or rigidly connected to, acoustic radiating means of the transducer, so that flexing forces and/or bending stresses to which the electroactive driver means may be subjected are substantially reduced and/or eliminated.
Another object of the present invention is to provide a transducer having acoustic radiating means including a flat member for generating acoustic energy, wherein the transducer and components thereof can be readily assembled/disassembled, repaired and/or replaced, especially as applied to components of the entire electroactive driver means, without need for special or sophisticated tooling or alignment procedures.